Apparatus and associated methods for switching between antennas in a multi-antenna receiver

ABSTRACT

Described herein are one or more apparatus, that at least partially synchronize with a first radio-frequency signal from a first antenna element, of an array of spatially distributed antenna elements in a multi-antenna array receiver, to determine the position of at least one of a repeated guard interval in the first radio-frequency signal from the first antenna element, the repeat occurring at a particular defined characteristic interval. The apparatus then use the determined position of the at least one guard interval in the first radio-frequency signal to switch to a second radio-frequency signal from a second antenna element, of the array of spatially distributed antenna elements in a multi-antenna receiver, and further determine a relative orientation of the multi-antenna receiver from a transmitter of the radio-frequency signals using characteristics determined for the first and second radio-frequency signals following the at least respective partial synchronizations.

RELATED APPLICATION

This application was originally filed as PCT Application No.PCT/IB2011/055792 filed Dec. 19, 2011.

TECHNICAL FIELD

The present disclosure relates to the field of radio-frequency (RF)signalling direction finding, associated methods, computer programs andapparatus. Certain disclosed aspects/embodiments relate to portableelectronic devices, in particular, so-called hand-portable electronicdevices which may be hand-held in use (although they may be placed in acradle in use). Such hand-portable electronic devices include so-calledPersonal Digital Assistants (PDAs) and tablet PCs.

The portable electronic devices/apparatus according to one or moredisclosed aspects/embodiments may provide one or more audio/text/videocommunication functions (e.g. tele-communication, video-communication,and/or text transmission (Short Message Service (SMS)/Multimedia MessageService (MMS)/emailing) functions), interactive/non-interactive viewingfunctions (e.g. web-browsing, navigation, TV/program viewing functions),music recording/playing functions (e.g. MP3 or other format and/or(FM/AM) radio broadcast recording/playing), downloading/sending of datafunctions, image capture function (e.g. using a (e.g. in-built) digitalcamera), and gaming functions.

BACKGROUND

In the field of mobile communications and localization/positioning,positioning and direction finding applications use antenna arrays,(which are also called multi-antennas). It is advantageous to use alarge number of antenna elements because the use of such antenna arraysimproves positioning accuracy, especially in indoor scenarios.Conventional antenna array receivers have to contain as many receiverchains as there are antenna elements in the array, leading to at leasthigh hardware complexity which grows linearly with the number of antennaelements in the array. To reduce hardware complexity in receivers usingantenna arrays, a circuit using a fast radio-frequency switch and asingle receiver chain can be used.

The listing or discussion of a prior-published document or anybackground in this specification should not necessarily be taken as anacknowledgement that the document or background is part of the state ofthe art or is common general knowledge. One or more aspects/embodimentsof the present disclosure may or may not address one or more of thebackground issues.

SUMMARY

In a first aspect, there is provided an apparatus comprising:

-   -   at least one processor; and    -   at least one memory including computer program code, the at        least one memory and the computer program configured to, with        the at least one processor, cause the apparatus to perform at        least the following:    -   perform at least partial synchronisation on a first        radio-frequency signal from a first antenna element, of an array        of spatially distributed antenna elements in a multi-antenna        array receiver, to determine the position of at least one of a        repeated guard interval in the first radio-frequency signal from        the first antenna element, the repeat occurring at a particular        defined characteristic interval;    -   use the determined position of the at least one guard interval        in the first radio-frequency signal to switch to a second        radio-frequency signal from a second antenna element, of the        array of spatially distributed antenna elements in a        multi-antenna receiver, the switch being performed from the        determined position of the at least one repeated guard interval,        or a position of a repeated guard interval, in the first        radio-frequency signal to perform at least partial        synchronisation to the second radio-frequency signal; and    -   determine a relative orientation of the multi-antenna receiver        from a transmitter of the RF signals using characteristics        determined for the first and second radio-frequency signals        following the at least respective partial synchronisations.

The apparatus may be configured to perform at least partialsynchronisation on the second radio-frequency (RF) signal after theswitch.

The apparatus may be configured to identify training symbols in therespective RF signals received from the respective antenna elements toperform said synchronisation.

Partial synchronisation may be considered to provide for one or more ofa primary coarse synchronisation fix and a secondary finesynchronisation fix. Fine synchronisation can also be considered toprovide for repeated synchronisation, i.e. tracking of an incomingsignal.

The apparatus may be configured to identify training symbols in thefirst RF signal to perform said (at least partial) synchronisation.

The apparatus may be configured to identify training symbols in thesecond RF signal to perform said (at least partial) synchronisation.

The apparatus may be configured to perform determination of the relativeorientation characteristics of the first and second radio-frequencysignals after the respective at least partial synchronisations.

The repeated guard intervals may have a particular length, wherein theswitching is performed to coincide with the beginning, middle or end ofthe particular length.

The RF signal may comprise a modulated carrier wave, modulated torepresent data.

Radio-frequency (RF) signalling is the raw signalling transmitted overthe air interface on the carrier i.e. before demodulation to remove thecarrier and decoding to retrieve the data content of the signalling

The first and second radio-frequency signals may represent repeatedinstances of the same data.

The first and second RF signals may represent one or more whole framesor partial frames, the frame comprising a sequence of training symbolsand payload data demarcated with respective repeated guard intervals.

The frame may represent a packetized burst in at least one of anorthogonal frequency division multiplex (OFDM) or wireless local areanetwork (WLAN) system.

The apparatus may be configured to use at least one common demodulationand decoding channel path in demodulating and decoding the respectivefirst and second radio-frequency signals.

The apparatus may be configured to switch the radio-frequency signalsfrom the respective antenna elements to use the at least one commondemodulation and decoding channel path to demodulate and decode therespective radio-frequency signals, the switch being performed from thedetermined position of the at least one repeated guard interval, or aposition of a repeated guard interval, in an radio-frequency signal froma previous antenna element.

The apparatus may be configured to use the at least one commondemodulation and decoding channel path in demodulating and decoding therespective first and second radio-frequency signals and wherein theapparatus is configured to determine the relative orientationcharacteristics using the at least one common demodulation and decodingchannel path.

The apparatus may be configured to use:

-   -   a first reference demodulation and decoding channel path        connected to a first reference antenna element; and    -   a second receiver demodulation and decoding channel path        connected to a second receiver antenna element,    -   wherein the first reference channel path is useable to        synchronise switching of the second receiver demodulation and        decoding channel path from the second receiver antenna element        to a further receiver antenna element.

The first reference antenna element may be the same reference antennaelement for all receiver elements to which the second receiver channelpath is switched.

The first reference antenna element for a given receiver element may beswitched so as to vary in accordance with the particular receiverantenna element currently in use.

The apparatus may be configured to determine the position of a repeatedguard interval by using the particular predefined intervalcharacteristic on the position of the at least one repeated guardinterval.

The relative orientation characteristics determined for the first andsecond radio-frequency signals, following the at least partialsynchronisations, may be comprise the respective phases and amplitudesof the first and second radio-frequency signals.

The apparatus may be configured to switch to radio-frequency signalsfrom further antenna elements from the spatially distributed antennaelements of the multi-antenna array receiver, the switch being performedfrom the determined position of the at least one repeated guardinterval, or a position of a repeated guard interval, in the firstradio-frequency signal, or the radio-frequency signal from the previousantenna element, to perform at least partial synchronisation to thefurther radio-frequency signal; and

-   -   determine a relative orientation of the multi-antenna receiver        from the transmitter using characteristics determined for a        plurality of the first, second and further radio-frequency        signals following the at least partial synchronisation.

The multi-antenna array receiver may be an OFDM receiver.

The apparatus may be configured for operating according to one or moreof OFDM, WLAN, 802.11a/g/n standards, LTE, WiMax, and the like.

The apparatus may be one or more of: an electronic device, a portableelectronic device, a laptop computer, a desktop computer, a mobilephone, a Smartphone, a tablet computer, a monitor, a personal digitalassistant, a digital camera, a watch, a server, or a module/circuitryfor one or more of the same.

In another aspect, there is provided a method comprising:

-   -   performing at least partial synchronisation on a first        radio-frequency signal from a first antenna element, of an array        of spatially distributed antenna elements in a multi-antenna        array receiver, to determine the position of at least one of a        repeated guard interval in the first radio-frequency signal from        the first antenna element, the repeat occurring at a particular        defined characteristic interval;    -   using the determined position of the at least one guard interval        in the first radio-frequency signal to switch to a second        radio-frequency signal from a second antenna element, of the        array of spatially distributed antenna elements in a        multi-antenna receiver, the switch being performed from the        determined position of the at least one repeated guard interval,        or a position of a repeated guard interval, in the first        radio-frequency signal to perform at least partial        synchronisation to the second radio-frequency signal; and    -   determining a relative orientation of the multi-antenna receiver        from a transmitter of the RF signals using characteristics        determined for the first and second radio-frequency signals        following the at least respective partial synchronisations.

In another aspect described herein, there is provided an apparatusconfigured to perform the steps of the above method aspect using asequencer.

In another aspect, there is provided a computer readable mediumcomprising computer program code stored thereon, the computer readablemedium and computer program code being configured to, when run on atleast one processor, perform at least the following:

-   -   performing at least partial synchronisation on a first        radio-frequency signal from a first antenna element, of an array        of spatially distributed antenna elements in a multi-antenna        array receiver, to determine the position of at least one of a        repeated guard interval in the first radio-frequency signal from        the first antenna element, the repeat occurring at a particular        defined characteristic interval;    -   using the determined position of the at least one guard interval        in the first radio-frequency signal to switch to a second        radio-frequency signal from a second antenna element, of the        array of spatially distributed antenna elements in a        multi-antenna receiver, the switch being performed from the        determined position of the at least one repeated guard interval,        or a position of a repeated guard interval, in the first        radio-frequency signal to perform at least partial        synchronisation to the second radio-frequency signal; and    -   determining a relative orientation of the multi-antenna receiver        from a transmitter of the RF signals using characteristics        determined for the first and second radio-frequency signals        following the at least respective partial synchronisations.

In another aspect there is provided an apparatus comprising:

-   -   a means for synchronising configured to perform at least partial        synchronisation on a first radio-frequency signal from a first        antenna element, of an array of spatially distributed antenna        elements in a multi-antenna array receiver, to determine the        position of at least one of a repeated guard interval in the        first radio-frequency signal from the first antenna element, the        repeat occurring at a particular defined characteristic        interval;    -   a means for switching configured to switch to a second        radio-frequency signal from a second antenna element, of the        array of spatially distributed antenna elements in a        multi-antenna receiver, using the determined position of the at        least one guard interval in the first radio-frequency signal to,        the switch being performed from the determined position of the        at least one repeated guard interval, or a position of a        repeated guard interval, in the first radio-frequency signal to        perform at least partial synchronisation to the second        radio-frequency signal; and    -   a means for determining configured to determine a relative        orientation of the multi-antenna receiver from a transmitter of        the RF signals using characteristics determined for the first        and second radio-frequency signals following the at least        respective partial synchronisations.

In another aspect described herein, there is provided a sequencerconfigured to be able to:

-   -   perform at least partial synchronisation on a first        radio-frequency signal from a first antenna element, of an array        of spatially distributed antenna elements in a multi-antenna        array receiver, to determine the position of at least one of a        repeated guard interval in the first radio-frequency signal from        the first antenna element, the repeat occurring at a particular        defined characteristic interval;    -   use the determined position of the at least one guard interval        in the first radio-frequency signal to switch to a second        radio-frequency signal from a second antenna element, of the        array of spatially distributed antenna elements in a        multi-antenna receiver, the switch being performed from the        determined position of the at least one repeated guard interval,        or a position of a repeated guard interval, in the first        radio-frequency signal to perform at least partial        synchronisation to the second radio-frequency signal; and    -   determine a relative orientation of the multi-antenna receiver        from a transmitter of the radio-frequency signals using        characteristics determined for the first and second        radio-frequency signals following the at least respective        partial synchronisations.

The sequencer may be a field programmable gate array configured to beuseable with or without one or more processors.

The present disclosure includes one or more corresponding aspects,embodiments or features in isolation or in various combinations whetheror not specifically stated (including claimed) in that combination or inisolation. Corresponding means for performing one or more of thediscussed functions are also within the present disclosure.

Corresponding computer programs for implementing one or more of themethods disclosed are also within the present disclosure and encompassedby one or more of the described embodiments.

The above summary is intended to be merely exemplary and non-limiting.

BRIEF DESCRIPTION OF THE FIGURES

A description is now given, by way of example only, with reference tothe accompanying drawings, in which:—

FIG. 1 illustrates an example according to the present disclosure.

FIG. 2 illustrates another example.

FIG. 3 illustrates another example.

FIG. 4 illustrates a frame of information.

FIG. 5 illustrate timing associated with a frame of information.

FIG. 6 illustrates a first example utilising a commondemodulator/decoder path.

FIG. 7 illustrates a second example utilising two demodulation/decodingpaths.

FIG. 8a illustrates an example of a synchronisation circuit.

FIG. 8b shows an example of switching times.

FIG. 9 illustrates a flowchart according to a method of the presentdisclosure.

FIG. 10 illustrates schematically a computer readable media providing aprogram according to an embodiment of the present disclosure.

FIGS. 11 and 12 illustrate various embodiments as implemented in exampleelectronic devices.

DESCRIPTION OF EXAMPLE ASPECTS/EMBODIMENTS

Angle of arrival (AoA) based indoor positioning systems require anantenna array at the receiver. In known multi-antenna receivers,converting the received signal into a digital baseband signal requiresone demodulator/decoder path for each antenna element. Consequently, thehardware complexity of such a solution grows linearly with the number ofantenna elements. This increases hardware size and weight as well as thecost of the receiver.

In contrast to telephony communication systems, it is not necessary toobtain the antenna signals simultaneously for AoA systems. The antennasignals can be obtained sequentially from different elements atdifferent times. This principle is used in, e.g. channel soundingmethods, or Bluetooth LE based indoor positioning systems, etc. Usingthe switching principle for unsynchronised, i.e. random access (CSMA)radio transmission requires real-time (RT) synchronisation of theantenna switching times with the received signal. Such systems do notcontinuously stream data, but transmit signals representing data inpacketized bursts.

To use the switching antenna receiver for wireless local area network(WLAN) signals requires a higher accuracy in the switching times asneeded for, say, Bluetooth signals for example. There is currently nosolution for real-time antenna switching synchronization for randomaccess broadband radio transmissions (e.g. WLAN IEEE802.11a,IEEE802.11g, IEEE802.11n). Described example embodiments will bedescribed in relation to WLAN implementations, but it will beappreciated by those skilled in the art that this process could beapplied to other OFDM systems.

In one or more embodiments described herein, there is provided anapparatus that, at least in some embodiments, comprises at least oneprocessor and at least one memory with computer program code storedthereon, the code being configured to, with the processor, cause theapparatus to perform particular steps to provide improvements in theabovementioned fields.

Firstly, the apparatus performs at least partial synchronisation on afirst radio-frequency (RF) signal from a first antenna element, of anarray of spatially distributed antenna elements in a multi-antenna arrayreceiver, to determine the position of at least one of a repeated guardinterval in the first radio-frequency (RF) signal from the first antennaelement, the repeat occurring at a particular defined characteristicinterval. Thus, the apparatus synchronises with signalling received viaa first antenna element based on the repeated occurrence of so-calledguard intervals in the signal.

These guard intervals are not provided to carry payload data (i.e.payload data being critical data of interest to a user) but to helpprovide for redundancy within data packets. These guard intervals occurregularly at predefined characteristic intervals, according to the OFDMstandard/protocol used in a given multi-antenna system.

Secondly, the apparatus uses the determined position of the at least oneguard interval in the first radio-frequency signal to switch to a secondradio-frequency signal from a second antenna element, of the array ofspatially distributed antenna elements in a multi-antenna receiver, theswitch being performed from the determined position of the at least onerepeated guard interval, or a position of a repeated guard interval, inthe first radio-frequency signal to perform at least partialsynchronisation to the second radio-frequency signal. Because the guardintervals provide redundancy, it is advantageous to switch (whereswitching is to be used for receiving signals from different antennaelements as in the present disclosure) to another antenna element duringreception of a guard interval instead of switching at some arbitrarytime, which could result in switching during reception of critical dataand therefore incurring data loss.

Thirdly, the apparatus determines a relative orientation of themulti-antenna receiver from a transmitter of the RF signals usingcharacteristics determined for the first and second radio-frequencysignals following the at least respective partial synchronisations. Byreceiving signals from different antenna elements that are spatiallydistributed, the slight variations in phase and amplitude of the signalsreceived by each antenna can be compared to establish the direction orrelative orientation of the signal source.

We will now describe a first example with reference to FIG. 1, whichshows an apparatus 100 comprising a processor 110, memory 120, input Iand output O. In this embodiment only one processor and one memory areshown but it will be appreciated that other embodiments may utilise morethan one processor and/or more than one memory (e.g. same or differentprocessor/memory types). For example, the memory 120 can be composed ofat least one block of ROM 120 a and at least one block of RAM 120 c. TheROM block 120 a allows for storage of data/computer program code (assoftware code represent by software code block 120 b) and the RAM block120 c also provides operating space (using RAM block 120 c) for theconnected processor 110 to utilise that software code from block 120 b.This particular configuration is illustrated with the dashed blocks ofFIG. 1. Such an arrangement where a processor utilises memory blocks 120a/b/c in such a way to perform operations specified by a computerprogram would be understood by a person skilled in the art.

In this embodiment the apparatus 100 is an application specificintegrated circuit (ASIC) for a portable electronic device 200 with atouch sensitive display 240 (as per FIG. 2 and later shown in FIGS. 11and 12). In other embodiments the apparatus 100 can be a module for sucha device, or may be the device itself, wherein the processor 110 is ageneral purpose CPU of the device 200 and the memory 120 is generalpurpose memory comprised by the device 200. It will be appreciated thatthe schematic illustration of apparatus 100 of FIG. 1 can be implementedas different types and configurations of apparatus, e.g. module, ASIC,some variations of FPGA, etc, and that this figure should not beunderstood to limit the possible implementations of the apparatus of thepresent disclosure. For example, it is possible to implement one or moreembodiments as FPGA arrangements where one or more processors are used,or even to provide arrangements that do not utilise any processors atall (e.g. using a sequencer).

The input I allows for receipt of signalling to the apparatus 100 fromfurther components, such as a multi-antenna receiver array like that ofthe multi-antenna array 260 in portable electronic device 200 of FIG. 2,or also from other components of portable electronic device 200 (likethe touch-sensitive display 240 in FIG. 2) or the like. The output Oallows for onward provision of signalling from within the apparatus 100to further components (e.g. back to multi-antenna array 260 forswitching of the array 260, or to the display 240 the like). In thisembodiment the input I and output O are part of a connection bus thatallows for connection of the apparatus 100 to further components.

The processor 110 is a general purpose processor dedicated toexecuting/processing information received via the input I in accordancewith instructions stored in the form of computer program code on thememory 120. The output signalling generated by such operations from theprocessor 110 is provided onwards to further components via the outputO.

The memory 120 (not necessarily a single memory unit) is a computerreadable medium (solid state memory in this example, but may be othertypes of memory such as a hard drive, ROM, RAM, Flash or the like) thatstores computer program code. This computer program code storesinstructions that are executable by the processor 110, when the programcode is run on the processor 110. The internal connections between thememory 120 and the processor 110 can be understood to, in one or moreembodiments, provide an active coupling between the processor 110 andthe memory 120 to allow the processor 110 to access the computer programcode stored on the memory 120.

In this embodiment the input I, output O, processor 110 and memory 120are all electrically connected to one another internally to allow forelectrical communication between the respective components I, O, 110,120. In this example the components are all located proximate to oneanother so as to be formed together as an ASIC, in other words, so as tobe integrated together as a single chip/circuit that can be installedinto an electronic device. In other embodiments one or more or all ofthe components may be located separately from one another (for example,throughout a portable electronic device like device 200 of FIG. 2 ordevice 300 of FIG. 3 and/or may provide/support other functionality,i.e. shared to provide different respective functionalities).

Apparatus 100 discussed above can be used as a component for anotherapparatus or device such as in FIG. 2 (or, in a more specific example,like a PDA as per FIG. 12—discussed later). FIG. 2 can be understood todepict a variation of apparatus 100 or a device 200 that incorporatesthe functionality of apparatus 100 spread throughout constituentcomponents. FIG. 3 can be understood to depict a variation of apparatus100 or a device 200 that actually incorporates apparatus 100 to provideits functionality. The integration and operation of apparatus 100 withindevices 200, 300 will become evident from the following. Although in anumber of embodiments the apparatus 100 is shown as configured as aprocessor and a memory, as stated above, in some embodiments a sequencercan be used (e.g. a field programmable gate array) that does notnecessarily utilise a processor for its operation. The implementation ofthe following functionality as a sequencer or FPGA will be appreciatedby someone skilled in the art.

We will now describe the functionality provided by apparatus 100 withreference to FIG. 4 which shows an OFDM frame according to the OFDMstandard for 802.11a/b/g/n wireless communications. This frame iscomposed of several components which are as follows:

-   -   (i) 10 short training symbols (STS)—the short training symbols        are, according to the standard, the features of the OFDM        signalling that OFDM receivers look for to establish a coarse        synchronisation fix on the received OFDM signalling (discussed        in more detail below). While these symbols provide for coarse        synchronisation, this can be considered to provide for at least        partial synchronisation with a given signal from a given antenna        element. Other components of the frame can provide for enhanced        synchronisation, but in any case at least partial        synchronisation is provided for by these short training symbols        STS;    -   (ii) first guard interval (GI1)—as already stated, guard        intervals do not carry payload data but are repeated lengths of        code that separate respective OFDM blocks of data within a given        frame. In the illustrated frame, each respective OFDM block is        preceded by a guard interval that is actually a copy of the last        800 ns of that particular OFDM block. In this case, GI1 precedes        2 long training symbols (LTS—which are discussed in more detail        below), which means that the last 800 ns worth of data of the 2        long training symbols is copied and used as the preceding guard        interval for those symbols. This is done as part of a given OFDM        standard at the receiver;    -   (iii) 2 long training symbols (LTS)—the long training symbols        LTS are, according to any given OFDM standard, the features of        the OFDM signalling that OFDM receivers use to establish a fine        synchronisation fix on the received OFDM signalling, i.e. to        further refine the coarse synchronisation fix achieved using the        short training symbols STS. This refinement of the        synchronisation can be understood to improve synchronisation        with a given signal, as the coarse synchronisation fix provided        by the short training symbols STS is not quite as accurate as        that which is achievable using the long training symbols LTS;    -   (iv) second guard interval (GI2)—another guard interval that        separates the 2 long training symbols LTS and the next OFDM        block;    -   (v) signal 1 symbol (SS)—This is a standard part of OFDM frames        and is well understood in the art. This is part of standard OFDM        protocols that control how the frame is used and interpreted.    -   (vi) third guard interval (GI3)—another guard interval that        separates the payload and service data (PL1—see below) and the        earlier signal symbol SS;    -   (vii) payload and service data (PL1)—this is the first instance        of actual data that is to be received and used in some way, e.g.        data relating to an Internet webpage being wirelessly streamed        in packetized bursts to a wireless communications device. The        training symbols can be considered to be a header to the real        data of interest that is being carried as payload data        (PL1-PLn);    -   (viii) fourth guard interval (GI4)—another guard interval; and    -   (ix) payload data (PL2)—second instance of actual data. The        frame may continue for a longer or shorter period of time, with        more or less payload data or other OFDM blocks contained        therein. This is just an example.

FIG. 5 illustrates the timing attributes of the different OFDM blockswithin the frame. The OFDM standard in this example provides a standarddefinition that the short training symbols STS must be 10 symbols long,each symbol being 0.8 microseconds long. Further standard-defineddefinitions apply to the long training symbols LTS, the guard intervalsGI1-4, the payload data PL1-2, etc. Other standards have otherstandard-defined definitions for their signal syntax.

If the direction from which the radio-frequency (RF) signallingoriginated is not important, the apparatus 100 can just receive anddemodulate the data of the signalling via a single antenna element. Incontrast, if the direction must be established, then a multi-antennareceiver is required to obtain information about the angle of arrival ofsignalling. Each element will receive a slightly different version ofthe transmitted OFDM signalling, and the subtle variations between thesignals received at each element (e.g. phase, amplitude differences etc)reflect the angle of arrival of the OFDM signalling.

In the art, this reception of data and performance of direction findingwould be done by providing demodulation/decoder chains for each andevery antenna element. This ensures that the data contained in the OFDMsignalling is received, demodulated and decoded for each and everyantenna element and reduces likelihood of data loss. To save costs, asingle common demodulation/decoder path can be used, but the switchingmust be done carefully to avoid switching during critical datareception.

FIG. 6 illustrates an example embodiment. The input and output I/O ofthe apparatus 100 is connected to a multi-antenna array 410 comprising aplurality of antenna elements 410 a-c (such arrays are well-known in theart). The apparatus 100 is also connected to a singledemodulation/decoder chain 420 for reading the OFDM data in thesignalling (such demodulation/decoder chains are also well-known in theart). Such chains typically have two mixers (421 a, b)—as well as alocal oscillator (422) and phase shifter (423)—two low-pass filters (424a, b), two AD converters (425 a, b) and one decoder (426) to provide anoutput to a determine of orientation component (427) though otherdesigns for such chains which provide equivalentfunctionality/functionalities are within the scope of the presentdisclosure.

The apparatus 100 in this example forms a synchronisation circuit 400for switching which antenna element of the array 410 is currently beingused for receiving OFDM signalling.

OFDM signalling is transmitted from a source at some distance and someunknown orientation from the example receiver of FIG. 6. A signal isreceived via a first antenna element 410 a of the multi-antenna thatrepresents the transmitted OFDM signalling. The short training symbolsSTS are always the same from frame to frame and for a given standard.Therefore, the synchronisation circuit 400 needs to monitor signalsreceived via a first antenna element 410 a to lock onto those signalsand perform a coarse (i.e. at least partial) synchronisation on thatsignal. The sequence of the short training symbols STS provides atraining preamble that is therefore used to detect the beginning of aOFDM frame, which in this case is a WLAN OFDM frame.

An autocorrelation function is used to determine the frame start i.e.the occurrence of the known short training symbols STS. Autocorrelationis the cross-correlation of a signal with itself. Informally, it is thesimilarity between observations as a function of the time separationbetween them. It is a mathematical tool for finding repeating patterns,such as the presence of a periodic signal (like repeating trainingsymbols) which could have been buried under noise, or identifying themissing fundamental frequency in a signal implied by its harmonicfrequencies. For example, because the short and long training symbolsare defined within a given standard it is possible to perform patternmatching to identify those training symbols from the raw IQ signal data,and/or the demodulated/decoded signal. The principle behindautocorrelation of signals is well understood in the art and variousdifferent approaches can be used to perform equivalent functionality inthis aspect.

An autocorrelation function can be also applied to find the exact timewhen a new symbol of a given OFDM block within the frame is started bypattern matching the signal with itself, for example, to spot rising orfalling edges that can indicate the beginning, middle, or end ofparticular symbols within the frame.

From this autocorrelation/pattern matching information, thesynchronisation circuit 400 establishes the start time for the framebased on the short training symbols STS, and can then know exactly wherethe long training symbols are to be expected to allow for a finesynchronisation fix with the signal. This fine/complete synchronisationneed not always be performed as in some instances a coarse/partialsynchronisation can be sufficient (e.g. with greater data redundancy,greater knowledge of the system, etc giving a greater margin for error).

In any case, once the synchronisation circuit 400 is synchronised tosome extent (whether partial or fully) with the signal from the firstantenna element 410 a, expected start times for each of the OFDM blockswithin the frame, inclusive of their respective preceding guardintervals, are therefore known from the given standard being used as thesyntax of each frame is predetermined according to each OFDM standard.

The first antenna element is therefore used for timing acquisition usingthe short training sequence (STS) in the beginning of the OFDM WLANframe. As the length of an OFDM block is known to be 4000 ns (see FIG.4), the beginning, middle, and/or end of any given OFDM block can beinferred with some accuracy from this starting time estimate.

The synchronisation circuit 400 then uses the determined position of theat least one guard interval GI1-4 in the first radio-frequency signal(received via the first antenna element 410 a) to switch to receiving asecond radio-frequency signal from a second antenna element 410 b of themulti-antenna array during a guard interval. Because the guard intervalsoccur at particular defined characteristic intervals based on the OFDMstandard, the synchronisation circuit 400 therefore knows the expectedposition of each guard interval GI1-4 within the received signal fromthe first antenna element 410 a from the start of a given frame.

After this, the synchronisation circuit 400 receives a second signalfrom second antenna element 410 b. The synchronisation circuit 400 cancontinue to switch again during a guard interval to further antennaelements (e.g. 410 c, or back to 410 a, etc) or even more antennaelements, or can use just two antenna elements (like 410 a and 410 bonly)

By repeatedly switching between antenna elements 410 a-c of the array410, the data contained in the transmitted OFDM signalling can keepbeing received, but the additional knowledge of phase and amplitudedifferences between reception at each of the antenna elements 410 a/b/ccan be gathered and used to determine a relative orientation of themulti-antenna receiver from a transmitter of the RF signals. In effect,reading the OFDM signalling from different antenna elements (410 a-c)allows for use of characteristics (e.g. phase and/or amplitude of therespective signals from each antenna element 410 a-c) determined for thefirst and second (or more) radio-frequency signals received viarespective antenna elements following the synchronisations on each ofthe elements. The direction of orientation component 427 can utilisethese characteristics to determine the relative orientation of the array410 to the transmission source.

Also, because the switch is being performed from the determined positionof the at least one repeated guard interval, or a position of a repeatedguard interval, in the first radio-frequency signal, this means that theswitching occurs during reception of non-critical data. Switching atsuch times helps to reduce the likelihood of critical data loss.

The apparatus 100 implemented as part of a synchronisation circuit 400therefore allows for signalling to be received via a first antennaelement 410 a of the array 410, then, at a time where critical data isnot going to be lost (during the guard interval) the apparatus 100causes switching to receiving signalling via a second antenna element410 b of the array. This means that the apparatus 100 has switched theantenna array 410 to receiving a second signal from another antennaelement (410 b or even 410 c) during a non-critical time.

In particular, because the synchronisation circuit 400 is causingswitching between antenna elements 410 a-c of the array 410 at timeswhen critical data will not be lost, only a single decoder/demodulatorchain 420 needs to be coupled to the antenna array 400. Every time theantenna array 410 is switched to pass on the received signal from adifferent antenna element 410 a/b/c, the received signal is providedonward to the decoder/demodulator chain 420 which can operate on thatreceived signal to extract data of interest.

In summary, by performing synchronisation with a signal received via afirst antenna element of an array, and switching (based on thatsynchronisation) to a second antenna element at a guard interval, it ispossible to ensure safe and accurate switching between signals fromdifferent antenna elements to thereby maintain integrity of criticaldata transmissions and also determine relative orientation of the arrayfrom the transmission source. All these advantages can also be achievedwhile simultaneously reducing receiver complexity as only a singledecoder/demodulator chain (as per 420) need be provided to successfullydecode/demodulate the data from the cumulated signals from each antennaelement (as per 410 a-c).

FIG. 7 illustrates a schematic of a further example. This example issimilar to that of FIG. 6 except that it also comprises anotherdemodulator/decoder chain 530 which is connected (non-switchably) to afirst reference antenna element 515. In contrast to the example of FIG.6, the synchronisation circuit 500 (performed in this example by aplurality of separate circuits—discussed below) continually receives anRF signal from a given transmitter via the first reference antennaelement 515. This first ‘reference’ demodulator/decoder chain 530provides a reference signal for maintaining a synchronisation fix on thesignal of interest.

The second receiver demodulation/decoder chain 520 and antenna array 510effectively operates in the same way as that of FIG. 6, i.e. switched bythe synchronisation circuit 500. Because the first reference chain 530is continually being synchronised with the OFDM signal being received bythe first reference antenna element 515, this helps to ensure that nocritical data is lost from the received transmission, whilstsimultaneously providing a reference for switching in the secondreceiver chain, i.e. reliably indicating when guard intervals should beoccurring in the received signalling, and when the synchronisationcircuit 500 should cause antenna elements 510 a-c to be switchedbetween. This can provide for enhanced calculation of optimal switchingtime and data integrity.

This particular synchronisation circuit 500 calculates the optimalswitching time by comparing portions of the raw IQ signal againstitself. A given guard interval GI3 occurs at a first time, and from thestandard and the training symbols it can be determined that the nextguard interval GI4 should occur 3.2 μs after GI3. Based on thisprinciple, two portions of the signal can be compared against each otherto try and perform pattern matching of those portions. While the patternof each guard interval will be reflective of the OFDM block thatparticular guard interval GI abuts, there will be common featuresbetween respective guard intervals given that they are the same lengthas each other, and always reflect the same portion (the last 0.8microseconds) of their corresponding OFDM blocks. As such, various partsof a guard interval such as leading edge, trailing edge (e.g. framestart, frame end, etc), and other such patterns will be similar andrecognisable between respective guard intervals.

Therefore, the similarity between the pattern of two signal segmentshaving the same length as the standard-defined guard interval (e.g. 0.8microseconds) can be computed and used to work out the likelihood ofthose two portions being two sequential guard intervals as there shouldbe a strong autocorrelation between two portions that are indeed guardintervals.

In operation, the moving power calculator 550 of the synchronisationcircuit 500 receives the real (Q) and imaginary (I) parts of a signalreceived from a first reference antenna element 515. It should bepointed out that in other applications for direction finding it has beenfound that using I and Q parts of a signal provides a particularlyadvantageous way of determining direction. The moving power calculator550 then calculates the power and pattern of two respective portions ofthe received signal, which can be used to provide an indication of wherethe end of a frame is located. This information is provided to theswitching time calculator 570.

The real and imaginary parts of the signal are also useable withpreamble autocorrelation circuit 560 which will compare the respectivepatterns to calculate the extent of the correlation between the twoportions. This can be used to provide an indication where the start of aframe is located. This information is then provided to the switchingtime calculator 570.

The moving power calculator 550 is continuously monitoring two portionsof the incoming signal spaced apart by a particular symbol length and/ortime and therefore constantly monitoring pattern matches. The preambleautocorrelation circuit 560 also receives the real and imaginary partsof the signal currently being received to perform its calculations.

The switching time calculator (which can be a processor-lessfinite-state machine) 570 receives the output from the moving powercalculator 650 and the preamble autocorrelation circuit 560 in order toestablish whether the conditions are met to elicit switching at aparticular time.

The maximum correlation value or values that occur for a given frame arelikely to indicate the times at which guard intervals have occurred andtherefore also indicate the optimal switching time. If the thresholdvalues are matched then the switching time calculator/finite-statemachine 570 will provide a switching signal S to cause switching to thenext antenna element, which in turn will restart calculations in advanceof the next switch to occur.

In addition, the cyclic prefix calculator 565 is configured to operateas described above to ‘search’ for the respective guard intervals in asignal. Once guard intervals have been identified this can provideinformation that is useable to adjust the calculated switching timebased on where the frame is identified to start and where it isidentified to end. In any case, these circuits (550, 560, 565) can eachco-operate together to allow for synchronisation of the switching of theantenna array with the frame and OFDM blocks within that frame beingreceived from a transmitter.

In another example, the moving power calculator 550/650 can calculatethe moving average of the magnitude squared difference signal for a timeperiod that is equivalent to the length of a standard guard interval(e.g. over a 0.8 microsecond period) to use as the basis for theautocorrelation.

When the synchronisation circuit 500 detects the end of thetransmission, i.e. the end of the frame, the apparatus returns to anidle state (and optionally goes back to the first antenna element 510a).

To summarise the operation of the synchronisation circuit 500 describedabove, these synchronisation circuits 500 are configured to move betweenthree different states to provide this functionality:

-   -   1) Idle state—The synchronisation circuit 500 stays in, or        returns, to the idle state when no signal is being received.    -   2) Acquisition state—The synchronisation circuit 500 moves to        the acquisition state if a new frame is received, and starts to        acquire a raw estimate of signal being received (e.g. raw IQ        data of the signalling, such as from the first reference antenna        element 515). Afterwards, the synchronisation circuit 500 moves        to the tracking state.    -   3) Tracking state—in the tracking state the synchronisation        circuit 500 measures the time difference between the current        switching time and what the synchronisation circuit 500        calculates to be the optimal switching time and corrects the        current switching time accordingly, e.g. using autocorrelation,        and/or monitoring for any corruption of data. For example, if        the last switching between two antennas is detected to have        caused a loss of data the synchronisation circuit 500 can modify        the switching time to correct for this to try and ensure that        the next switch does not cause loss of data.

FIG. 8a shows another embodiment of a switching/synchronisation circuit600 that is similar to that of synchronisation circuit 500 shown in FIG.7. Circuit 600 also comprises a threshold storage circuit 680 whichstores information about when switching is to occur, i.e. in response toa particular threshold being met by the autocorrelation between the tworespective portions of the signal. These thresholds can beuser-determined, predetermined by the present system or another system,or (by way of a learning algorithm) altered in response to particularsituations to tailor the switching response.

In contrast to FIG. 7, which has the autocorrelation circuit 560 (whichdetects the short training symbols STS) and the cyclic prefixautocorrelation circuit 565 (which detects the respective guardintervals GI) are combined into one autocorrelation circuit 660.Furthermore, respective circuits 650, 660, 670 can be reset by anexternal signal to restart the process for taking new sets of readings,and all the respective circuits 650, 660, 670 are in communicationwith/being driven by a common clock signal (see clock management 690).Furthermore, in this preferred implementation the threshold storage 680can be reprogrammed at runtime. Functionally, the example of FIG. 8aoperates in substantially the same way as the arrangement shown in FIG.7.

An advantage of any of these examples is that the right time of thesymbol starts can be found also in the event where a frame start hasbeen detected inaccurately. If there is a slip in the symbols such thatdata is lost from one chain, a correction can be made to find the righttiming on when to switch the receiver antenna array while not losingdata because the reference antenna has still been receiving the data.

Another advantage that this switching system provides is that switchingcan occur up to 800 ns earlier or later than the exact start of theguard interval GI, and data integrity can still be maintained. Forexample, If the switching occurs within the 800 ns after the start ofthe guard interval GI, then switching still occurs within thenon-critical data of the guard interval and no critical data is lost (asdescribed above). If the switching occurs in the 800 ns before a givenguard interval (e.g. in the last 800 ns of the preceding payload data,such as PL1) the data that would otherwise be lost from that region canbe substituted by the received guard interval GI3 corresponding to thatof the payload data PL1.

In an optional embodiment, shown in FIG. 8b , antenna switching canoccur at an arbitrary but known time in an OFDM block (a block containsthe GI and the OFDM symbol). In this embodiment the next switchingshould occur after at least one complete undisturbed OFDM block has beenreceived, though in some embodiments this may not be possible at certaininstances due to certain system constraints. In this way it isguaranteed that at least one undisturbed OFDM-symbol is acquired withina switching interval.

In the example of FIG. 7, the reference antenna element 515 isnon-switchably connected to the reference demodulator/decoder chain. Ina variation of this embodiment of FIG. 7 (whether using synchronisationcircuit 500 or 600) the reference demodulator/decoder chain is actuallyswitchably connected to a multi-antenna array (which can be the same (ordifferent) to that of multi-antenna array 510 of FIG. 7). Instead of thereference demodulator/decoder chain only receiving signals from a staticreference antenna element (515), this chain can also be switched toincrementally change the reference antenna element from which signalsare being received by the reference demodulator/decoder chain.

This can be advantageous in examples where a multi-antenna array isshaped in such a way that errors could occur due to an increasingdistance or phasing issues between a static reference antenna elementand whichever antenna element of an array is being used as switchingprogresses through the respective elements of that array. For example,for an array shaped in a circle/with radial symmetry it can beadvantageous to incrementally switch both the reference antenna elementand the receiver antenna element so as to cause the reference antennaelement to ‘follow’ the receiver antenna element presently being usedaround that array, though this is just one example. Other array typesmay benefit from different switching arrangements. In any case, both thereference demodulator/decoder chain and the receiver demodulator/decoderchain can be made to be flexible to allow for optimisation for use witha given array.

It should also be noted that each of synchronisation circuits 500/600can be implemented as a finite-state machine, or as a sequencerconfigured to be used with or without one or more processors.

FIG. 9 illustrates a flowchart summarising the methods of operationdescribed above.

701—Receive signal via a particular antenna element of an array—thiswill start receiving signalling from a first antenna element.

702—Synchronise with the signal from that element—This might optionallyinvolve using information from a reference antenna.

703—Determine position of guard intervals within signal from thatelement based on the synchronised signal.

704—Cause switching to a further antenna element of the array at a timewhere critical data will not be lost from that signalling—this is basedon the position of the guard intervals within the signalling asdiscussed above. This will result in switching to another antennaelement, from where step 701 is repeated for that new antenna element.705—Receive signal via a reference antenna element of an array—this isan optional step for when two demodulator/decoder chains are used asdiscussed above.706—Synchronise with the signal from that (reference antenna)element—This is used to help aid the synchronisation step 702 and alsoused to feed the step of demodulation/decoding the data of interest.707—Demodulate/decode signals from each antenna element—for the purposesof determining a relative orientation of the array from a transmissionsource, this is an optional step.708—Determine a relative orientation of the array from a transmitterusing characteristics of each of the antenna signals—the characteristicdifferences between signals from respective antenna elements allow fororientation between the receiver array and a particular transmitter tobe determined.

FIG. 10 illustrates schematically a computer/processor readable media1000 providing a program according to an embodiment of the presentinvention. In this example, the computer/processor readable media is adisc such as a digital versatile disc (DVD) or a compact disc (CD). Inother embodiments, the computer readable media may be any media that hasbeen programmed in such a way as to carry out an inventive function. Thecomputer program code may be distributed between the multiple memoriesof the same type, or multiple memories of a different type, such as ROM,RAM, Flash, hard disk, solid state, etc.

It will be appreciated that any of the above embodiments would beuseable in various different devices, particularly mobile devices withwireless communications capability like mobile telephones like that ofFIG. 11, and touch screen devices like that shown in FIG. 12. Forexample, in other example embodiments, the apparatus 100 or any of theexamples given above can be provided in such a device 200. Apparatus 100may be provided as a module (shown by the optional dashed line box inFIG. 2 and FIG. 3) for a mobile phone or PDA or audio/video player orthe like. Such a module, apparatus or device may just comprise asuitably configured memory and processor (as per FIG. 1—see also theapparatus 100 within device 300 of FIG. 3).

In the example of FIG. 2, the functionality offered by each of thecomponents in the example of FIG. 1 is shared between other componentsand the functions of the device of FIG. 2. In some examples the device200 is actually part of a mobile communications device like a mobiletelephone of FIG. 11, PDA of FIG. 12, tablet PC, or laptop, or the like.

In this case, the device 200 comprises a display device 240 such as, forexample, a Liquid Crystal Display (LCD) or touch-screen user interface.The device 200 is configured such that it may receive, include, and/orotherwise access data. For example, device 200 can comprise acommunications unit 250, such as a receiver, transmitter, and/ortransceiver, in communication with a multi-antenna array 260 forconnecting to a wireless network and/or a port (not shown) for acceptinga physical connection to a network, such that data may be received viaone or more types of networks. This example embodiment comprises amemory 220 that stores data, possibly after being received viamulti-antenna 260 or port or after being generated at the user interface230. The processor 210 may receive data from the user interface 230,from the memory 220, or from the communication unit 250. Regardless ofthe origin of the data, these data may be outputted to a user of device200 via the display device 240, and/or any other output devices providedwith apparatus. The processor 210 may also store the data for later userin the memory 220.

The device 200 comprises processor 210, memory 220, interface 230,display 240 (in certain embodiments, the interface 230 and the display240 may be combined, for example, via a touch sensitive display),communications unit 250, multi-antenna 260 all connected together viacommunications bus 280. The communications unit 250 can be, for example,a receiver, transmitter, and/or transceiver, that is in communicationwith a multi-antenna 260 for connecting to a wireless network and/or aport (not shown) for accepting a physical connection to a network, suchthat data may be received via one or more types of networks. Thecommunications (or data) bus 280 can be seen, in one or moreembodiments, to provide an active coupling between the processor 210 andthe memory (or storage medium) 220 to allow the processor 210 to accessthe computer program code stored on the memory 220.

The memory 220 comprises the computer program code in the same way asthe memory 120 of apparatus 100, but may also comprise other data thatcan be useable by the (or other) processor/processors/memory/memories.For example, the memory 220 can (in some embodiments) be able to storeother data, possibly after being received via antenna 260 or port orafter being generated at the user interface 230. The processor 210 mayreceive data from the user interface 230, from the memory 220, or fromthe communication unit 250. Regardless of the origin of the data, thesedata may be outputted to a user of device 200 via the display device240, and/or any other output devices provided with apparatus. Theprocessor 210 may also store the data for later user in the memory 220.

As has been discussed, FIG. 2 illustrates schematically a device 200(such as a portable mobile telephone or portable electronic device)comprising the apparatus 100 (or functionality of the apparatus 100distributed throughout its components) as described above. FIG. 3illustrates another such implementation in device 300.

The device 300 may be an electronic device (including a tablet personalcomputer), a portable electronic device, a portable telecommunicationsdevice, or a module for any of the aforementioned devices. The apparatus100 can be provided as a module for such a device 300, or even as aprocessor/memory for the device 300 or a processor/memory for a modulefor such a device 300. The device 300 also comprises a processor 385 anda storage medium 390, which are electrically connected to one another bya data bus 380. This data bus 380 can be seen to provide an activecoupling between the processor 385 and the storage medium 390 to allowthe processor 380 to access the computer program code.

The apparatus 100 is first electrically connected to an input/outputinterface 370 that receives the output from the apparatus 100 andtransmits this onwards to the rest of the device 300 via data bus 380.Interface 370 can be connected via the data bus 380 to a display 375(touch-sensitive or otherwise) that provides information from theapparatus 100 to a user. Display 375 can be part of the device 300 orcan be separate.

The device 300 also comprises a processor 385 that is configured forgeneral control of the apparatus 100 as well as the rest of the device300 by providing signalling to, and receiving signalling from, the otherdevice components to manage their operation (e.g. to receive signalsfrom and allow switching of a multi-antenna array).

The storage medium 390 is configured to store computer code configuredto perform, control or enable the making and/or operation of theapparatus 100. The storage medium 390 may also be configured to storesettings for the other device components. The processor 385 may accessthe storage medium 390 to retrieve the component settings in order tomanage the operation of the other device components. The storage medium390 may be a temporary storage medium such as a volatile random accessmemory. On the other hand, the storage medium 390 may be a permanentstorage medium such as a hard disk drive, a flash memory, or anon-volatile random access memory. The storage medium 390 could becomposed of different combinations of same or different memory types.

It will be appreciated to the skilled reader that any mentionedapparatus/device/server and/or other features of particular mentionedapparatus/device/server may be provided by apparatus arranged such thatthey become configured to carry out the desired operations only whenenabled, e.g. switched on, or the like. In such cases, they may notnecessarily have the appropriate software loaded into the active memoryin the non-enabled (e.g. switched off state) and only load theappropriate software in the enabled (e.g. on state). The apparatus maycomprise hardware circuitry and/or firmware. The apparatus may comprisesoftware loaded onto memory. Such software/computer programs may berecorded on the same memory/processor/functional units and/or on one ormore memories/processors/functional units.

In some embodiments, a particular mentioned apparatus/device/server maybe pre-programmed with the appropriate software to carry out desiredoperations, and wherein the appropriate software can be enabled for useby a user downloading a “key”, for example, to unlock/enable thesoftware and its associated functionality. Advantages associated withsuch embodiments can include a reduced requirement to download data whenfurther functionality is required for a device, and this can be usefulin examples where a device is perceived to have sufficient capacity tostore such pre-programmed software for functionality that may not beenabled by a user.

It will be appreciated that the any mentionedapparatus/circuitry/elements/processor may have other functions inaddition to the mentioned functions, and that these functions may beperformed by the same apparatus/circuitry/elements/processor. One ormore disclosed aspects may encompass the electronic distribution ofassociated computer programs and computer programs (which may besource/transport encoded) recorded on an appropriate carrier (e.g.memory, signal).

It will be appreciated that any “computer” described herein can comprisea collection of one or more individual processors/processing elementsthat may or may not be located on the same circuit board, or the sameregion/position of a circuit board or even the same device. In someembodiments one or more of any mentioned processors may be distributedover a plurality of devices. The same or different processor/processingelements may perform one or more functions described herein.

It will be appreciated that the term “signalling” may refer to one ormore signals transmitted as a series of transmitted and/or receivedelectrical/optical signals. The series of signals may comprise one, two,three, four or even more individual signal components or distinctsignals to make up said signalling. Some or all of these individualsignals may be transmitted/received by wireless or wired communicationsimultaneously, in sequence, and/or such that they temporally overlapone another.

With reference to any discussion of any mentioned computer and/orprocessor and memory (e.g. including ROM, CD-ROM etc), these maycomprise a computer processor, Application Specific Integrated Circuit(ASIC), field-programmable gate array (FPGA) or similar (such asCPLD—Complex Programmable Logic Device; PSoC—Programmable System onChip; ASIC—Application Specific Integrated Circuit, etc), and/or otherhardware components that have been programmed in such a way to carry outthe inventive function.

The applicant hereby discloses in isolation each individual featuredescribed herein and any combination of two or more such features, tothe extent that such features or combinations are capable of beingcarried out based on the present specification as a whole, in the lightof the common general knowledge of a person skilled in the art,irrespective of whether such features or combinations of features solveany problems disclosed herein, and without limitation to the scope ofthe claims. The applicant indicates that the disclosedaspects/embodiments may consist of any such individual feature orcombination of features. In view of the foregoing description it will beevident to a person skilled in the art that various modifications may bemade within the scope of the disclosure.

While there have been shown and described and pointed out fundamentalnovel features of the invention as applied to preferred embodimentsthereof, it will be understood that various omissions and substitutionsand changes in the form and details of the devices and methods describedmay be made by those skilled in the art without departing from thespirit of the invention. For example, it is expressly intended that allcombinations of those elements and/or method steps which performsubstantially the same function in substantially the same way to achievethe same results are within the scope of the invention. Moreover, itshould be recognized that structures and/or elements and/or method stepsshown and/or described in connection with any disclosed form orembodiment of the invention may be incorporated in any other disclosedor described or suggested form or embodiment as a general matter ofdesign choice. Furthermore, in the claims means-plus-function clausesare intended to cover the structures described herein as performing therecited function and not only structural equivalents, but alsoequivalent structures. Thus although a nail and a screw may not bestructural equivalents in that a nail employs a cylindrical surface tosecure wooden parts together, whereas a screw employs a helical surface,in the environment of fastening wooden parts, a nail and a screw may beequivalent structures.

The invention claimed is:
 1. An apparatus comprising: at least oneprocessor; and at least one memory including computer program code, theat least one memory and the computer program configured to, with the atleast one processor, cause the apparatus to perform at least thefollowing: perform at least partial synchronisation on a firstradio-frequency signal from a first antenna element, of an array ofspatially distributed antenna elements in a multi-antenna arrayreceiver, to determine the position of at least one of a repeated guardinterval in the first radio-frequency signal from the first antennaelement, the repeat occurring at a particular defined characteristicinterval; use the determined position of the at least one guard intervalin the first radio-frequency signal to switch to a secondradio-frequency signal from a second antenna element, of the array ofspatially distributed antenna elements in a multi-antenna receiver, theswitch being performed from the determined position of the at least onerepeated guard interval, or a position of a repeated guard interval, inthe first radio-frequency signal to perform at least partialsynchronisation to the second radio-frequency signal; and determine arelative orientation of the multi-antenna receiver from a transmitter ofthe radio-frequency signals using characteristics determined for thefirst and second radio-frequency signals following the at leastrespective partial synchronisations.
 2. The apparatus of claim 1,wherein the apparatus is configured to perform at least partialsynchronisation on the second radio-frequency signal after the switch.3. The apparatus of claim 1, wherein the apparatus is configured toidentify training symbols in the respective radio-frequency signalsreceived from the respective antenna elements to perform saidsynchronisation.
 4. The apparatus of claim 1, wherein the apparatus isconfigured to identify training symbols in the first radio-frequencysignal to perform said synchronisation.
 5. The apparatus of claim 1,wherein the apparatus is configured to identify training symbols in thesecond radio-frequency signal to perform said synchronisation.
 6. Theapparatus of claim 1, wherein the apparatus is configured to performdetermination of the relative orientation characteristics of the firstand second radio-frequency signals after the respective at least partialsynchronisations.
 7. The apparatus of claim 1, wherein the repeatedguard intervals have a particular length, and wherein the switching isperformed to coincide with the beginning, middle or end of theparticular length.
 8. The apparatus of claim 1, wherein theradio-frequency signal comprises a modulated carrier wave, modulated torepresent data.
 9. The apparatus of claim 1, wherein the first andsecond radio-frequency signals represent repeated instances the samedata.
 10. The apparatus of claim 1, wherein the first and secondradio-frequency signals represent a whole frame, the frame comprising asequence of training symbols and payload data demarked with respectiverepeated guard intervals.
 11. The apparatus of claim 1, wherein theframe represents a packetized burst in at least one of an OFDM or WLANsystem.
 12. The apparatus of claim 1, wherein the apparatus isconfigured to use at least one common demodulation and decoding channelpath in demodulating and decoding the respective first and secondradio-frequency signals.
 13. The apparatus of claim 12, wherein theapparatus is configured to switch the radio-frequency signals from therespective antenna elements to use the at least one common demodulationand decoding channel path to demodulate and decode the respectiveradio-frequency signals, the switch being performed from the determinedposition of the at least one repeated guard interval, or a position of arepeated guard interval, in an radio-frequency signal from a previousantenna element.
 14. The apparatus of claim 12, wherein the apparatus isconfigured to use the at least one common demodulation and decodingchannel path in demodulating and decoding the respective first andsecond radio-frequency signals and wherein the apparatus is configuredto determine the relative orientation characteristics using the at leastone common demodulation and decoding channel path.
 15. The apparatus ofclaim 1, wherein the apparatus is configured to use: a first referencedemodulation and decoding channel path connected to a first referenceantenna element; and a second receiver demodulation and decoding channelpath connected to a second receiver antenna element, wherein the firstreference channel path is useable to synchronise switching of the secondreceiver demodulation and decoding channel path from the second receiverantenna element to a further receiver antenna element.
 16. The apparatusof claim 15, wherein the first reference antenna element is the samereference antenna element for all receiver elements to which the secondreceiver channel path is switched.
 17. The apparatus of claim 15,wherein the apparatus is configured to switch the first referenceantenna element so that the reference antenna element for a givenreceiver element varies in accordance with the particular receiverantenna element currently in use.
 18. The apparatus of claim 1, whereinthe apparatus is configured to switch to radio-frequency signals fromfurther antenna elements from the spatially distributed antenna elementsof the multi-antenna array receiver, the switch being performed from thedetermined position of the at least one repeated guard interval, or aposition of a repeated guard interval, in the first radio-frequencysignal, or the radio-frequency signal from the previous antenna element,to perform at least partial synchronisation to the furtherradio-frequency signal; and determine a relative orientation of themulti-antenna receiver from the transmitter using characteristicsdetermined for a plurality of the first, second and furtherradio-frequency signals following the at least partial synchronisation.19. A method comprising: performing at least partial synchronisation ona first radio-frequency signal from a first antenna element, of an arrayof spatially distributed antenna elements in a multi-antenna arrayreceiver, to determine the position of at least one of a repeated guardinterval in the first radio-frequency signal from the first antennaelement, the repeat occurring at a particular defined characteristicinterval; using the determined position of the at least one guardinterval in the first radio-frequency signal to switch to a secondradio-frequency signal from a second antenna element, of the array ofspatially distributed antenna elements in a multi-antenna receiver, theswitch being performed from the determined position of the at least onerepeated guard interval, or a position of a repeated guard interval, inthe first radio-frequency signal to perform at least partialsynchronisation to the second radio-frequency signal; and determining arelative orientation of the multi-antenna receiver from a transmitter ofthe RF signals using characteristics determined for the first and secondradio-frequency signals following the at least respective partialsynchronisations.
 20. A non-transitory computer readable mediumcomprising computer program code stored thereon, the computer readablemedium and computer program code being configured to, when said computerprogram code is run on at least one processor, cause an apparatus toperform at least the following: performing at least partialsynchronisation on a first radio-frequency signal from a first antennaelement, of an array of spatially distributed antenna elements in amulti-antenna array receiver, to determine the position of at least oneof a repeated guard interval in the first radio-frequency signal fromthe first antenna element, the repeat occurring at a particular definedcharacteristic interval; using the determined position of the at leastone guard interval in the first radio-frequency signal to switch to asecond radio-frequency signal from a second antenna element, of thearray of spatially distributed antenna elements in a multi-antennareceiver, the switch being performed from the determined position of theat least one repeated guard interval, or a position of a repeated guardinterval, in the first radio-frequency signal to perform at leastpartial synchronisation to the second radio-frequency signal; anddetermining a relative orientation of the multi-antenna receiver from atransmitter of the RF signals using characteristics determined for thefirst and second radio-frequency signals following the at leastrespective partial synchronisations.